The invention relates generally to the heating of liquids, and specifically to those devices wherein rotating elements are employed to +generate heat in the liquid passing through them. Devices of this type can be usefully employed in applications requiring a hot water supply, for instance in the home, or by incorporation within a heating system adapted to heat air in a building residence. Furthermore, an economic portable steam generator could be useful for domestic applications such as the removal of winter salt from the underside of vehicles, or the cleaning of fungal coated paving stones in place of the more erosive method by high-pressure water jet.
Of the various configurations that have been tried in the past, types employing rotors or other rotating members are known, one being the Perkins liquid heating apparatus disclosed in U.S. Pat. No. 4,424,797. Perkins employs a rotating cylindrical rotor inside a static housing and where fluid entering at one end of the housing navigates through the annular clearance existing between the rotor and the housing to exit the housing at the opposite end. The fluid is arranged to navigate this annular clearance between static and non-static fluid boundary guiding surfaces, and Perkins relies principally on the shearing effect in the liquid, causing it to heat up. A modern day successor to Perkins is shown in U.S. Pat. No. 5,188,090 to James Griggs. Like Perkins, the Griggs machine employs a rotating cylindrical rotor inside a static housing and where fluid entering at one end of the housing navigates past the annular clearance existing between the rotor and the housing to exit the housing at the opposite end. The device of Griggs has been demonstrated to be an effective apparatus for the heating of water and is unusual in that it employs a number of surface irregularities on the cylindrical surface of the rotor. Such surface irregularities on the rotor seem to produce an effect quite different than the forementioned fluid shearing of the Perkins machine, and which Griggs calls hydrodynamically induced cavitation. Also known as the phenomena of water hammer in pipes, the ability of being able to create harmless caviation implosions inside a machine without causing the premature destruction of the machine is paramount. The Giggs machine would seem to take time to reach steady state conditions before reaching maximum efficiency, due most likely to the difficulty of such surface irregularities becoming sufficiently primed with fluid at stary up. Such surface irregularities, at the commencement of rotor rotation, may be largely empty of fluid, and as such, there is likely a time lag before sufficient fluid is, by the severe turbulent flow conditions, in the gap between rotor and housing, able to enter into these surface irregularities to produce the desired hydrodynamically induced vatitational heating of the fluid flowing through the machine. A further feature of Griggs is that the maximum effect is limited by the size of volume pocket void that exists for each surface irregularity. For instance, a surface irregularity in the form of a drilled hole has a certain diameter and depth which determines the maximum quantity of fluid it can hold. During operation of the Griggs machine, this quantity of fluid is reduced, most likely reduced quite substantially in order to create the desire effect of a very low-pressure region in and about the hole. For certain applications, there may be advantage through the deployment of deeper holes in the rotor, as compared to the depth of holes taught by Griggs, for improved shock wave transmissions from the cavitiation implosion zones to maximum power efficiency in performance. Furthermore, the protection of bearings and seals against deterioration caused by high temperatures and pressures in the fluid entering and exiting the machine is important. The use of detachable bearing/seal units mounted externally to the housing is a known solution that is used to space the bearing and seal members further away from the hot regions of the machine. However, there would be advantage if some or all the bearings and seals could be disposed in a cooler region in the machine, thereby saving the additional complication and expense of having to use such detachable bearing/seal units. There therefore is a need for a new solution whereby the effects of high temperatures and pressures are less harmful to such bearings and seals.
The present invention seeks to improve on some or all of the above mentioned limitation of earlier machines without undue complication and whereby the cavitational heating of the fluid by shock wave transmissions from the cavitation implosion zones can be maximized.
There is also a need for a new solution whereby such surface irregularities confronting the annular chamber, as well as any internal voids or cavities within the rotor itself, can be primed with fluid prior to the commencement of rotation of the rotor.